Campaign to investigate better forecasts of weather processes in winter

Winter storms developing over the North Atlantic Ocean and extending to the shores of Western Europe tend to reach hurricane-like wind speeds, cause damage in the million range and, in extreme cases, put the life of people at risk. Last week, winter storm "Elli" showed the impact such weather systems can have even in Germany: train cancelations, traffic chaos, and school closures.

"So far, it's very challenging to accurately predict where and when such extreme weather events will strike and how strong their impact will be," says Dr. Annika Oertel from KIT's Institute of Meteorology and Climate Research—Troposphere Research (IMKTRO). Many of the physical processes that result in high-impact weather events in Europe have their origin over the Atlantic Ocean—an area insufficiently monitored by conventional observation systems so far.

The large-scale measurement campaign NAWDIC (North Atlantic Waveguide, Dry Intrusion, and Downstream Impact Campaign) aims to contribute to more reliable weather forecasts and climate models based on detailed data collected by aircraft and ground-based observation.

"We are planning to take our measurements exactly in those regions for which indications suggest systematic shortcomings in our models," says Dr. Andreas Schäfler from the German Aerospace Center (DLR), whose responsibilities include the coordination of the research flights.

How does the Atlantic Ocean shape the weather in Europe?

In particular, the researchers want to know how dry, cool air sinking downward from high altitudes—also termed dry intrusions—affects atmospheric circulation, cloud structures, and wind development.

"If these dry air masses break through to the ground, they can produce strong gusts, turbulences, and severe weather," says Dr. Julian Quinting from the Institute of Geophysics and Meteorology of the University of Cologne. The North Atlantic plays a key role as a source of moisture for much of the precipitation in Europe.

"We know, however, that the processes involved with moisture absorption over the Atlantic Ocean, especially during dry intrusion events, have not been represented accurately in weather-forecast models yet. We want to change that," adds Quinting.

Searching for clues over the Atlantic Ocean

The campaign relies on the German research aircraft HALO, which is operated by the DLR. State-of-the-art remote sensing instruments, such as the WALES water vapor Lidar and the HEDWIG wind Lidar, measure moisture and wind beneath the aircraft up to a height of approx. 13 kilometers. This way, they document both the water vapor transport rate and the interactions between the atmosphere and the ocean.

Advantageously, HALO is a long-range aircraft so that weather systems across the Atlantic Ocean can be sampled. Ground-based observations with KITcube, KIT's mobile atmosphere observation system, which has been in operation already since November in Brittany, add to the aircraft measurements.

KITcube is a network of remote sensing instruments that can capture atmospheric processes in a height ranging from a few meters up to 10 kilometers. More than one hundred national and international scientists will be busy during the next weeks, planning the flights taking off from Ireland, monitoring measuring devices, and coordinating the activities with international partners.

Thanks to long-term planning over the last six years, in coordination with the World Meteorological Organization (WMO), the researchers managed to link up NAWDIC with other meteorological measurement campaigns in Northern America. Thus, up to ten research aircraft will be operating simultaneously in January and February—between the Pacific Ocean and Europe.

"This is a unique opportunity to comprehensively analyze the dynamics and the interactions of weather systems," says Oertel.

Provided by Karlsruhe Institute of Technology